Add Ward Harold's REST API draft to docs

These API docs, although still in draft, are very valuable and should live in git. I took the liberty to move them into git and did some reformatting as well as minor edits. I've also re-formatted `attrib_types.md`, leaving the other two files to Ward or someone else if we agree on this format.

Rendered pages:

* [README.md](https://github.com/jamestyj/crowbar/blob/api-draft/doc/devguide/api/README.md)
* [attrib_types.md](https://github.com/jamestyj/crowbar/blob/api-draft/doc/devguide/api/attrib_types.md)
* [attrib.md](https://github.com/jamestyj/crowbar/blob/api-draft/doc/devguide/api/attrib.md) (unformatted)
* [barclamp.md](https://github.com/jamestyj/crowbar/blob/api-draft/doc/devguide/api/barclamp.md) (unformatted)


See Ward's email at http://lists.us.dell.com/pipermail/crowbar/2013-March/002877.html for details.